1. Field of the Disclosure
The instant disclosure relates to a heat dissipation system; in particular, to a heat dissipation system with a rotation speed control circuit.
2. Description of Related Art
In the modern society of information technology, a computer system has become one of indispensable information tools, and whether for a desktop personal computer (PC), a laptop PC, or server, a clock operation of a central processor is increasing, and which results in an increasing heat dissipation, and a demand for heat dissipation appears to be more and more important. In prior art, a fan is a mainly way for the heat dissipation, and under the consideration of energy-saving and noise reduction, there are multiple methods of controlling a rotation speed developed for the heat dissipation fan used for the central processor, wherein a special method is to use two sets of signal sources to control the rotation speed of the fan.
U.S. Pat. No. 8,157,536 disclosed a speed adjustment circuit and a control system for the heat dissipation fan. The control system for the heat dissipation fan consists of a rotation speed control circuit, a rotation speed control circuit, an AND gate, and a logic circuit. The rotation speed control circuit is for sensing a temperature of heat dissipation fan in order to generate a first temperature-controlled signal. The rotation speed control circuit is for receiving a system control signal to produce a second temperature-controlled signal. The AND gate is coupled to the rotation speed control circuit and the rotation speed control circuit, and is for conducting an operation on the first temperature-controlled signal and the temperature-controlled signal to produce a first control signal. The rotation speed control circuit includes a first node, a second node, a receiving end, a first resistor, a second resistor, a third resistor, a capacitor, a transistor, an oscillating signal generator and a comparator. The receiving end is coupled to the AND gate for receiving the first control signal. The first resistor has one end coupled to a voltage source and another end coupled to the first node. The second resistor has one end coupled to the first node, and another end coupled to the second node. The third resistor has one end coupled to the second node, and another end coupled to a ground terminal. The capacitor has one end coupled to the first node, and another end coupled to the ground terminal. The transistor includes a first end coupled to the receiving end, and a second end coupled to the second node, and a third end coupled to the ground terminal for controlling to a signal link from the second end to the third end according to the signal of the first end. The oscillation signal generator is for producing an oscillation signal. The comparator includes a first input terminal coupled to the first node, a second input terminal coupled to the oscillation signal generator, and an output terminal for comparing a signal of the first node and the oscillation signal and outputting a second control signal through the output terminal. The logic circuit is coupled to the output end of the comparator and the heat dissipation fan for driving the heat dissipation fan according to the second control signal.
However, there are following disadvantages in the rotation speed control circuit and the control system for the heat dissipation fan of the U.S. Pat. No. 8,157,536. There are many pins required and it is likely to result in a fluctuating rotation speed caused by a variation of the external passive elements. Furthermore, it is less easy for the user to adjust the rotation speed curve flexibly since the method disclosed in the U.S. Pat. No. 8,157,536 is to construct circuits and systems by way of analogy.